I wouldn't say it deterred me away from them I just always feel I need these crazy torque servos when I can probably save some money and just utilize what I have laying around ! I love the 1270 in my 35% stuff!

And for those that don't understand the leverage principal, weaker fits the bill. Either way it is said the amount of oz-in at the control surface is the same, further from the servo center = weaker on the control surface side!! But I suspect you know what I am referring to and just don't like how I say it.

And if you want to play around, download the excel file I posted and look at the first 3 tabs - you can model the effect of different length servo arms and control horns without needing to do the math.

Generally setting up the lengths so that the servo is always using as close to its full +/- 60degree travel regardless of the surface throw is ideal for maximizing both leverage and control resolution. Like others Ive even used bellcranks at time in scale builds.

Ahh guilty.... I was just flying a .60 glow plane with 8611a's in it. Even the throttle servo. Just happened to 5 of them sitting there not doing anything.

Ive done this too. I'm building a quarter scale BUSA Triplane and I'm putting a set of HS5625s in it that I have lying around from an old 3D profile. But the tripe would probably fly just fine on S3004s

My point about not recommending BLS172/DS8711/HS7950 class servos to new guys with their first 30cc is partially about avoiding useless overgkill - but I also do it so as not to scare off a newcomer telling them they need $1000 of servos in their first plane.

Back in the late 80s my 22 lb 62cc plane had 42 oz-in servos on each surface. Not much was available back then and I did not know better. I flew that plane for many hundred flights without a problem. There was probably a lot of blow down, but I wasn't flying precision aerobatics or 3D. I would not recommend that today, but many of the suggested torques seem to be over kill. I also find it strange that the manufactures have increased the suggested torques five fold, but strength of the structure that the servo is mounted to has not changed.

Hi guys,
I am trying to estimate how much torque is required to deflect a given control surface. Is there a simple (ie not based on advanced math) way to calculate this?

What I am trying to do is to activate the control surfaces of my full size plane (single seat) with servos. I have split the control surfaces (ailerons, flaps and rudder) into a number of separate panels both so that I can tailor each panel's deflection to correspond to the lift distribution of the wing/rudder, but also to make servo activation more manageable.

The benefits of controlling the control surfaces with a RC transmitter are quite exciting. I'd like to leverage the huge benefits of all the mixing which is available on today's RC transmitters. I will build in a full cable-activated backup to a separate control stick in case of radio failure. But I'm not expecting to use it. Modern RC kit is pretty reliable.

For example, I am working with the following actual numbers for one of my aileron control surfaces:
Span: 8.7 inches
Chord: 5 inches
Deflection: 35 deg
Speed: 155 mph

The big question is, using the above parameters, what size servo would I need to do the job?

Another more demanding control surface is at the rudder:
Span: 10 inches
Chord: 8.2 inches
Deflection: 30 deg
Speed: 155mph

Anyone care to give me a hand with this?

Regards,
Duncan

Brother, if you're looking here for these kinds of answers, you've already failed! I am not saying this to slight anyone here, but you are only giving us partial information, and to be honest, your intention to use RC servos on a full size bird is unrealistic at best. Your request is far beyond the scope of this forum. Consult some professional engineers who can help you. Good luck and fly safe!

Back in the late 80s my 22 lb 62cc plane had 42 oz-in servos on each surface. Not much was available back then and I did not know better. I flew that plane for many hundred flights without a problem. There was probably a lot of blow down, but I wasn't flying precision aerobatics or 3D. I would not recommend that today, but many of the suggested torques seem to be over kill. I also find it strange that the manufactures have increased the suggested torques five fold, but strength of the structure that the servo is mounted to has not changed.

I flew a 1/4 scale citabria for over 1000 logged flights with 148 futabas back in the day.. I got tired of a cd whining at me so I cut the dowel joining the elevator halves together and put a second elevator servo in it.. Shortly after that I quit logging my flights but It was in my hangar for 6 more years after which a buddy thumbed it in doing a flat spin..
It was set up with 45degrees of throw on all surfaces and I tossed it around as hard is I could...

nope..... we put way more servo in than we actually need. Also a servo that if stalled, wont smoke check or strip the gears is just as important as overall strength. I have been flying for over 40 years and have never had a 148 futaba fail... would i put one on my 3.3 carf yak. no. well wait there is one on the choke...

And for the original poster. Back in the day some friends of mine working on the guidance system for a very commonly used uav that is flown all over the world today used seikos on a varieze and also on another old homebuilt they bought to make the test flights to make sure the guidance and hi zoot satellite remote contrill would work. the backup radio was a bone stock futaba super 7 on ham band...

For a manned setup you probably want a full disconnect on the servo system so you wouldn't have to overcome them if something locked up.. of course several experimental autopilot systems out there require you to overcome the servo when its not in use.. you aren't treading any new ground other than hanging your butt out there to use an rc transmitter.. but wait you aren't... the navy used to make safety pilots ride along when training early drone operators back in the 50s. course then it was somebody elses butt hanging out as the operator was on the ground...